The present invention relates in general to ionization detectors, and more particularly to a calibration apparatus for testing ionization detectors. In accordance with the invention there is provided a predictable technique for simulating the presence of particles of combustion in the chamber or chambers of an ionization detector. The ionization detectors may be of the type shown in U.S. Pat. Nos. 4,021,671 and 4,121,717 and my co-pending application Ser. No. 959,102, filed Nov. 9, 1978.
U.S. Pat. Nos. 4,021,671 and 4,121,718 show the use of a particle capturing member for altering ionic current flow between the electrodes of an ionization chamber. This member is meant to be adjusted and maintained in some preset position. On the other hand, in accordance with the present invention there is provided a calibration means and method to simulate the presence of particles of combustion within the chamber or chambers of an ionization detector. The calibration means preferably has a rest position and is only temporarily moved to a particle simulating position for test purposes.
To accomplish the calibration in accordance with this invention there is provided means associated with the detector for temporarily altering the ionization current flowing between the electrodes so as to simulate the presence of particles of combustion within the chamber.
One important object of the present invention is thus to provide a calibration means and associated method for simulating the presence of particles of combustion within the chamber or chambers of an ionization detector.
Another object of the present invention is to provide such a means and method capable of providing a predictable simulation of the presence of particles of combustion.
Still another object of the present invention is to provide calibration means and method in accordance with the preceding objects and which can be accomplished quite quickly and easily.
To accomplish the foregoing and other objects of this invention there is provided an ionization detector having a chamber, electrodes associated with the chamber and an ionization source which is preferably a Beta ionization source. In accordance with the invention apparatus is provided for calibrating the detector to simulate the presence of particles of combustion. There are disclosed herein a number of different embodiments for accomplishing this purpose. In accordance with one embodiment probe means are provided extending into the chamber and having a first fixed position wherein the ionization current is unaltered and a second temporary position wherein the ionization current is lower to simulate particles of combustion. In this embodiment the probe may have two zones associated therewith including a conductive zone and a less conductive zone. The probe being rotatable to expose either zone toward the ionization current path. In accordance with another embodiment of the invention means are provided for supporting the ionization source and moving the source support means to move the source temporarily from a rest position to a position laterally from the ionization path. In still another embodiment of the present invention the calibration is provided by employing deflectable means supported within the chamber and having a first fixed position and a second temporary position. The first and second positions define different geometries for the detector chamber wherein the ionization current is altered to simulate particles of combustion by means of this change in chamber geometry. The deflecting means may include a tensioning member and manual actuating means for operating the tensioning member. This member may be located at virtually any position within the chamber to change the geometry (volume) thereof. The deflectable member is also preferably constructed with wings or the like about the source to collimate the radiation emanating into the chamber.
In accordance with the method of the present invention again, this method is practiced in association with a detector having a chamber, electrodes associated with the chamber and a radioactive source disposed at some position within the chamber. The method may also be practiced with a dual chamber arrangement or possibly even a triple chamber arrangement as disclosed in my U.S. Pat. No. 4,121,718. In accordance with the method means are associated with the chamber with said means capable of assuming one of two different positions. In accordance with the method the means may be maintained in a first position representative of a normal operating position for the detector and is movable to a temporary position for simulating the presence of particles of combustion.